The present invention relates to an orthopaedic prosthesis, and more particularly to a prosthesis with an enhanced surface finish for more secure fixation.
The precoating of prosthetic implants with a polymer coating is disclosed in U.S. Pat. No. 4,491,987 to Park and in U.S. Pat. Nos. 4,336,618; 4,365,359; 4,281,420; and 4,280,233 to Raab. In addition, U.S. Pat. No. 4,283,799 to Pratt, Jr., et al. discloses a method of implanting a prosthesis which includes precoating the skeletal cavity and implant stem, allowing both to cure, then applying further cement to the cavity before insertion of the stem. U.S. Pat. No. 4,514,865 to Harris also discloses an embodiment (see FIGS. 6 and 7 of Harris) in which an implant stem is precoated with a film of cement.
Numerous types of texturing are known for use on prosthetic implants. The following are representative of such texturing:
U.S. Pat. No. 4,608,053--Keller PA1 U.S. Pat. No. 4,608,052--Van Kampen, et al. PA1 U.S. Pat. No. 4,549,319--Meyer PA1 U.S. Pat. No. 4,535,487--Esper, et al. PA1 U.S. Pat. No. 4,530,116--Frey PA1 U.S. Pat. No. 4,430,761--Nierderer, et al. PA1 U.S. Pat. No. 4,261,063--Blanquaert PA1 U.S. Pat. No. 4,199,824--Nierderer PA1 U.S. Pat. No. 3,894,297--Mittelmeier, et al. PA1 U.S. Pat. No. 2,718,228--Van Steenbrugghe PA1 European Application No. EP 0 169 976 Al--Griss PA1 European Application No. EP 0 158 534 A2--Freeman PA1 European Application No. EP 0 131 178 A2--Link PA1 European Application EP 0 025 814 A1--Seidel, et al. PA1 Swiss Patent No. 560,042--Locke
Heretofor, prosthetic implants including a precoat of a polymer coating have been incorporated on an untextured surface. While U.S. Pat. No. 4,491,987 describes a pretreatment of the implant surface which is to be coated, this pretreatment of sulfuric acid, sandblasting, or the like is to prepare a fresh "roughened" surface to improve the bonding between the prosthesis and the polymer coating. However, it is noted that this "roughening" of the surface generally does not provide any substantial roughening which is visible to the eye without magnification. Accordingly, the surface is still generally smooth to the eye and does not provide any surface texturing to the implant. Precoating of an implant with a polymer coating increases the shear (sliding) strength and increases the tension (pulling) strength of an implant over an uncoated implant. In addition, precoating enhances the bond of the precoated implant to bone cement upon implantation with cement, improving the bonding over an uncoated implant.
Texturing for the sake of this specification is defined to be a rough or unsmooth surface which is visible to the eye without magnification, often referred to in the art as "macrotexturing." Such texturing of implant surfaces has been widely used as indicated by the above-listed patents regarding texturing. Texturing of an implant surface also tends to increase the shear strength over an untextured implant surface; however, texturing provides only a small increase in tension strength.
U.S. Pat. No. 4,566,138 to Lewis, et al., is also cited for general information. It includes an implant with a plurality of acrylic spacers adhered to a porous outer surface. The acrylic spacers provide a uniform space between the bone and prosthetic device to uniformly control the thickness of cement. The acrylic spacers are raised stubs covering only a small portion of the porous surface and such spacers are not a coating.